Separation of olefins from mixed hydrocarbon streams has long been a subject of research and process development efforts. This field includes such widespread applications as recovery of ethylene from steam cracker effluents or dilute refinery streams, C.sub.2 and C.sub.3 splitting, and recovery of butene-1 from mixed C-4 streams. One of the valuable olefins which can be separated out of a C-4 hydrocarbon stream is isobutylene. Isobutylene is valuable, among other uses, as a reactant in the preparation of high octane ethers such as methyl t-butyl ether and ethyl t-butyl ether, as well as ethylene and propylene glycol ethers.
In Chem Systems, Topical Reports, Vol. II, p. 1 (1988 Program), September 1989 there is discussed the recovery of butene-1 by complexation.
The use of complexing agents in solution for complexation of olefins to separate them from paraffins is addressed in U.S. Pat. Nos. 3,401,112 and 3,449,240 to Shell. Other patents describe olefin-paraffin separation by means of a selective complex formation. See U.S. Pat. Nos. 3,517,080 and 3,517,081 to Monsanto.
Research has demonstrated the removal of ethylene from dilute streams with cuprous containing complexes in aromatic solvents. See U.S. Pat. Nos. 3,592,865; 3,651,159 and 3,754,047 to Esso Research and Engineering. To review additional research in this area, see Gottesman, R. T. "A New Process for Separation of Ethylene from Low Grade Gas Streams," Technology Exchange, Chicago, Ill. (February 1977) and Gutierrez, A. P. et al. "ESEP-A Process for the Recovery of Ethylene" paper presented at the 175th ACS Meeting, Anaheim, Calif. (Mar. 12-17, 1978). An attractive process for ethylene recovery from a cat cracker off-gas was reviewed in Chem. Systems, PERP Third Quarterly Report, Section 3.00 (1978). Other complexing solutions and complexing agents incorporated into solid adsorbents and membranes are disclosed in U.S. Pat. No. 3,828,398 to Esso, U.S. Pat. No. 4,025,574 to Phillips, U.S. Pat. No. 4,545,966 to Walker and U.S. Pat. No. 3,979,280 to Deutsche Texaco.
In an article by Ho, N. S., Winston, Doyle, G., Savage, D. S. and Pruett, R. L. I.E.C. Res. 1988, 27, p. 334, there is described the use of a complexing solution for the separation of C.sub.2 -C.sub.5 olefins and linear .alpha.-olefins from internal and branched olefins of the same carbon number. The complexing solution is covered in U.S. Pat. No. 4,471,152 to Esso.
In the Chem Systems, Topical Reports, Vol. II reference above at page 4, it is indicated that the complexing solution of U.S. Pat. No. 4,471,152 works best for separating ethylene and in the last paragraph there is reference to the "suppression of the complexation of internal and branched olefins." Therefore this technology teaches away from benefits in attempting to separate isobutylene. This technology is of special interest in the separation of .alpha.-olefins and, thus, more separation is expected of butene-1 and butene-2. In Section 1.22, Ibid. there is a description of the application of copper complexation technology to recovery of butene-1 from a steam cracker C-4 stream. At page 7, last paragraph it is stated this technology is selective for butene-1 compared to isobutylene and all other C-4 components.
At subtitle 1.31 on page 10, Ibid. it is stated "isobutylene and butadiene are seen to be virtually inseparable from butene-1." Technologies are discussed for butene-1 recovery.
J.P. 59,051,224-A (to Maruzen) discloses isobutylene separation from C-4 hydrocarbon distillate fraction by countercurrent reaction with ethylene glycol in the presence of a cation exchange catalyst.
In related copending applications, Ser. Nos. 07/396,209 and 07/410,168 incorporated herein in their entirety by reference, methods are described for the preparation of ethylene and propylene glycol ethers from isobutylene and the corresponding glycol over an acidic montmorillonite clay catalyst or an acidic heterogeneous or homogeneous catalyst.
J.P. 55,053,228 discloses a method for the preparation of ethylene glycol tertiary-butyl ether by reacting ethylene glycol with isobutylene in the presence of a strongly acidic cation exchange resin.
In J.P. 63,250,336 there is described a method for the preparation of propylene glycol tert-butyl ether by reacting propylene glycol with isobutylene in the presence of a strong acidic cation-exchange resin and tert-butanol.
The separation of particular components of C-4 streams such as isobutylene, butene-1, 1,3-butadiene, etc. in good yield and purity is obviously a desirable goal in the art. It would be especially helpful if it were possible to separate isobutylene using an efficient, commercially attractive process. The isobutylene isolated could be used to produce valuable solvents such as propylene glycol and ethylene glycol monobutyl ethers.
There does not appear to be any art suggesting the separation of isobutylene from a C-4 hydrocarbon fraction using a heteropoly acid on an inert support.
It has been discovered that heteropoly acid on an inert support such as titania can be used to separate isobutylene from a C-4 fraction in two steps. It is an object of the present invention to separate isobutylene in good yield and regenerate glycol. Other objects will become apparent to those skilled in the art from the following description.